1. Field of the Invention
This invention relates to a process for producing one-package room temperature curable organopolysiloxane compositions having improved extrusion and slump properties in the compound or uncured state, curable in the presence of moisture, and suitable as sealants.
2. Prior Art
RTV organopolysiloxane compositions of the one-package type are well known in the art which cure into silicone rubber at room temperature in the presence of moisture. They are widely used in a variety of industrial fields including mechanical, electrical and building fields as sealing agents, adhesives, potting agents, framing materials, automotive FIPG, etc.
When sealants of RTV compositions in the uncured state are applied in practice, such factors as ease of discharge or extrusion and sag-control are important. It is then a common practice to add thixotropy control agents for the sag-control purpose.
Illustratively, U.S. Pat. Nos. 4,261,758 and 4,100,129 disclose RTV compositions having polyoxyalkylenes added as the sag-control agent, and U.S. Pat. No. 4,301,269 discloses an RTV composition having the reaction product between a polyoxyalkylene and a functional silane added as the sag-control agent.
These RTV compositions are generally prepared by mixing a base polymer, filler, sag-control agent, and plasticizer, finally blending a crosslinking agent, and dispersing the ingredients uniformly, or by previously reacting a functional silane with a base polymer at its end and thereafter, mixing a filler and sag-control agent with the base polymer.
However, the RTV compositions prepared by the above procedures have the problem that the sag-control agent, which is essentially a parting component, adversely affects the adhesion and if blended in larger amounts, can adversely affect the ease of extrusion of the composition. The addition of the sag-control agent leads to the complication of the manufacturing process, adding to the cost of manufacture and adversely affecting the sealant properties. As a countermeasure, JP-A 41361/1990 discloses a process for preparing an RTV polyorganosiloxane composition by mixing a hydroxyl group-bearing polyorganosiloxane with a ketoxime group-bearing organosilane as the crosslinking agent, and thereafter, mixing finely divided silica and a curing catalyst therewith. This composition is insufficient in anti-slump or sag-control properties and ease of extrusion when a filler having a relatively high specific gravity, typically calcium carbonate is used, or in the case of a different crosslinking system.
Therefore, an object of the present invention is to provide a process for preparing a one-package RTV organo-polysiloxane composition having sag-control, ease of extrusion, and improved sealing properties, through simple steps and at a low cost.